Direct access storage devices (DASD) have become part of everyday life, and as such, expectations and demands continually increase for greater speed for manipulating and holding larger amounts of data. To meet these demands for increased performance, the mechanical assembly in a DASD device, specifically the Hard Disk Drive (HDD) has undergone many changes.
In order for an HDD to hold more data, advances in the magnetic recording heads as well as the disk media on which the data is written have undergone major advances in the past few years. One factor in determining the amount of data that can be stored in an HDD is the ability of the magnetic recording head to write closely spaced data tracks onto the disk surface.
The magnetic recording head is fabricated to physical dimensions that typically enable the magnetic recording head to write a data track to a specified width. The track width will determine how close the data tracks can be written. One of the more critical dimensions of the magnetic recording head that influences track width is known as the pole-tip width. The pole-tip is the magnetic material of the magnetic recording head that is closest to the disk. The pole-tip allows magnetic flux to emanate from the magnetic recording head and into the disk.
The pole-tip width can be measured directly by inspecting the surface of the magnetic recording head that is exposed to the disk surface. Measuring pole-tip width does not always predict the resulting track width. There are anomalies in the fabrication of magnetic recording heads that can cause the heads to write a wider track than expected, or can cause the written track center to be different from the pole-tip center.
It is important in the development phase of a new HDD product to identify if a newly designed magnetic recording head is writing tracks of specified width, and writing tracks on center. Both wide written tracks and off-centered tracks will adversely affect previously written adjacent tracks.
The phenomenon of a magnetic recording head writing a wide track is known as “track squeeze.” The phenomenon of a head that writes off-center is known as Adjacent Track Interference or ATI. The corrective action for each can be different, and it is important to the development of the magnetic recording head to determine which phenomenon is occurring to prescribe the proper corrective action. The ATI identification methods of today mistakenly identify heads with track squeeze as heads with ATI.
With today's test methods, it is not possible to determine whether a magnetic recording head that is adversely affecting previously written tracks is a head that has track squeeze or ATI. What is needed is a test method for detecting the difference between track squeeze and ATI in a repeatable and accurate manner.